Method of producing a sealing-tight joint between two tubes on different materials

ABSTRACT

A method of producing a sealing tight joint between two tubes one of which has a greater wall thickness than the other. The thinner tube has a collar formed on it which will engage a circumferential groove in the end of the thicker tube when placed in end-to-end relationship. A ring shaped to conform with the collar is placed inside it. A sleeve is slid over the two tubes, this sleeve having an inwardly extending flange which engages the ring and holds it and the collar against the end of the thicker tube. After welding the collar in place, the thicker tube is worked so as to expand it axially so that the grooved end tightly engages the collar.

United States Patent Bernard et a]. 45 Sept. 19, 1972 [5 METHOD OFPRODUCING A SEALING- 3,434,194 3/ 1969 Whittaker et al ..29/523 TIGHTJOINT BETWEEN TWO TUBES 3,520,561 7/1970 Rininger ..285/286 X ONDIFFERENT MATERIALS 3,534,988 10/1970 Lindsey ..29/507 X [72] Inventors:Jean Andre Bernard, Barga; Adamo 1,703,037 2/1929 Heck ..29/516 X RenatoFaraoni, Rance both of 2,545,527 3/1951 Maxwell ..29/523 UX Italy3,100,742 8/1963 McGeary et al ..29/480 3,112,564 12/1963 Murray..29/470.5 [73] Assignee: European Atomic Energy Community (Eur-atom),Luxemb r FORElGN PATENTS 0R APPLICATIONS [22] Filed: Jan. 19, 1970811,060 8/1951 Germany ..285/187 [211 App]' 4147 Primary ExaminerCharlieT. Moon Attorney- Stevens, Davis, Miller & Mosher [30] ForeignApplication Priority Data Jan. 24, 1969 Belgium ..P 1211 [57] ABSTRACT Amethod of producing a sealing tight joint between U-S. CI. tw tubes oneof has a greater wall thickness 29/523, 285/173, 285/236 than the other.The thinner tube has a collar formed [5 CL 1 1 ..B23k on engage acircumferential groove in the [58] Fleld of Search ..285/173, 382,382.], 382.4, end of the thicker tube when placed in end to end 285/3825286; 29/4705 relationship. A ring shaped to conform with the collar 480is placed inside it. A sleeve is slid over the two tubes, this sleevehaving an inwardly extending flange which [56] References C'ted engagesthe ring and holds it and the collar against the UNITED STATES PATENTSend Of the thicker tube. After welding the collar in place, the thickertube is worked so as to expand it ax- 448,717 3/1891 f "285/3345 X iallyso that the grooved end tightly engages the collar. 1,573,103 2/1926Toml1nson..'. ..285/382.2 X 2,984,899 5/1961 Richter et al. ..285/286 X4 Claims, 1 Drawing Figure PATENTEDsEP 19 I912 METHOD OF PRODUCING ASEALING-TIGHT JOINT BETWEEN TWO TUBES ON DIFFERENT MATERIALS Thisinvention relates to a method of making a joint between two tubes ofdifferent materials and to joints i made by this method.

In the specification of our co-pending application Ser. No. 719,066filed Apr. 5, 1968, now U.S. Pat. No. 3,59l,9l8 there is described andclaimed a method of making an end-toend joint between two tubes in whichone tube (herein called the thick tube) has at least at its end portionto be joined a wall thickness greater than that of the other tube(herein called the thin tube). In that method the end face of the thicktube is formed with at least one circumferential grooveor rib, the thintube is formed with an external or internal flange or collar around itsend to be joined to abut the end face of the thick tube, a sleeve isfitted outside or inside an end portion of the thick tube, and thesleeve extends over the adjacent end portion of the thin tube. Thesleeve has a circumferential step which supports the flange or collar onthe side remote from the thick tube and has a corresponding shape toclamp the flange or collar in the groove or grooves or over the rib orribs. The sleeve is welded to the thick tube at a location spaced fromthe end of that tube and the thickness of the wall of the thick tube ismechanically reduced in a zone between the weld and the end of the tubethereby to effect differential endwise expansion of the thick tube andsleeve and to clamp the flange or collar between the step and the endface of the thick tube. This method (which will be referred tohereinafter as a method hereinbefore defined of making an end-to-endjoint between two tubes) enables a joint forming a tight seal to be madebetween two tubes of different materials, one of the tubes having a thinwall. The joint may for example be used in a primary circuit of anuclear reactor where tightness against leakage under pressure andthermal changes are important.

In the particular construction described in the specification of theaforementioned application, the thin tube has a collar, which may forexample be C- shaped in section in a radial plane but may be of othershapes. The end of the thick tube has a groove compatible with the shapeof the collar. The surface of the flange on the sleeve which bearsagainst the collar was shaped to be compatible with the shape of thecollar. This arrangement had the disadvantage that this flange on thesleeve required machining to a complex shape. Even so, when the flangecollar and groove are in contact under high pressure, the surfaces incontact are still relatively small in area. It is an object of thepresent invention to provide an improved method of making a joint of thekind hereinbefore defined.

In accordance with the present invention, in the method hereinbeforedefined of making a joint between two tubes, the surface of the flangeon the sleeve which faces said collar is made frustoconical and anintermediate ring is placed between this flange and the collar, the ringhaving its face towards the flange formed as a frustoconical surfacecorresponding to that on the flange and having on the opposite face asurface adapted to fit the collar.

The intermediate ring is preferably made from a material having acoefficient of thermal expansion substantially the same as that of thetube formed with a groove and that of the sleeve. Preferably also it hasat least equivalent mechanical properties, in particular compressivestrength.

The following is 'a description of one embodiment of the inventionreference being made to the accompanying drawing which shows a sectiontaken along an axial plane through the tubes to be connected.

Referring to the drawing, there is shown a first tube 1 (the thick tube)and a second tube 2 (the thin tube) made of a material different fromthat of the thick tube 1. The 'two tubes 1, 2 are to be connected to oneanother with a sealing-tight joint. The tube 1 is formed, adjacent thejoint, with a thickened portion 3 and the end face of the tube 1 isformed with a groove 4. The end of the tube 2 is formed by any knownmethod with a flange or collar 5. In the drawing the collar is C- shapedbut it can have any other shape for example it may be Z-shaped orU-shaped. However the shape of the collar and the groove have to becompatible with one another so that the collar can be forced tightlyinto the groove.

A sleeve 6 made of a material having a coefficient of thermal expansionsubstantially the same as that of the tube 1 and having a flange 7, hasan internal diameter such that the sleeve 6 can be fitted over the tube1 with a sliding fit. The flange 7 has a frustoconical face 8 on thesurface facing the collar 5. This conical face forms an angle of 45 to60 with the inside cylindrical surface of the sleeve 6. Between thisconical face and the collar 5 there is inserted a ring 12, preferablymade of a material having a coefficient of thermal expansion close tothat of the tube 1 and sleeve 6. This ring 12 has mechanical properties,particularly strength in compression, at least equivalent to that of thetube 1 and sleeve 6 but preferably higher. The ring 12 bears on flange 7by way of a frustoconical face 14 similar to that of the face 13 on theflange. lts opposite face has a surface shaped similar to that of thecollar 5.

To produce the sealing-tight joint, the sleeve 6 is introduced so thatits face 13 comes into free abutment with the ring 12 and the oppositeface of the ring 12 is close to or abutting the collar 5. There may be aclearance of the order of 0.1 mm. The tube 1 and sleeve 6 are thenwelded as shown at 9 without prestress in either. The assembly is thenmounted in a support 10 and the thickened portion 3 is expanded bya tubeexpander roller, indicated at 11, thus producing an axial elongation ofthe portion 3 relative to sleeve 6 which pressurizes the differentmembers. The material of the thickened portion 3 is so elongated thatthe tube end and groove 4 move towards the right as shown in the drawingand compress the collar between the end groove 4 and the ring 12 whichis itself compressed against the surface 13 of the flange. The collar 5isthus firmly retained in place between the groove and the ring thusachieving a satisfactory sealing tightness. The sleeve 6 is preferablyof considerable axial length, so that the collar can be tightened in asatisfactory controllable manner, and a reserve of resilient deformationcan be stored which is made available without the joint beingthermo-mechanically stressed. The pre-stressing produced by themechanical expansion may be such that sealing pressure is unloaded onlywhen the temperature of the whole internal member drops by a value ofthe order of 50 C relative to the sleeve. This therefore ensures thatthe joint behaves very satisfactorily when subjected to thermal shocks.Using the present invention, compared with the method described in theaforementioned US. Pat. No. 3,591,918, there are particular advantages.Instead of the flange 7 on the sleeve having to be machined to make itfit collar 5, there is only need for a simple turning operation toproduce a frustoconical surface. It is much easier to provide the faceon the ring 12 with a surface adapted to fit that of the collar than itis to machine the sleeve. Thus there are considerable advantages fromthe manufacturing point of view. Also due to compression resulting fromelongation of the inner tube 1 (following expansion of the thickenedportion 3) radial deformation of the ring 12 has the effect of furtherimproving the seal. It has been found that joints produced by the methoddescribed above have given sealing tightness of up to Lussecs,corresponding to the limit of sensitivity of a leak detector of the massspectrometer type.

We claim:

1. A method of making an end-to-end joint between a first tube having athin wall and a second tube having at least at its end portion to bejoined a wall thickness greater than that of the first tube, comprising:

a. forming the first tube with a collar around the end to be joined toabut the end face of the second tube;

b. placing a ring over said collar, said ring having one face adapted tofit the surface of the collar and the other face with a frusto-conicalsurface;

. fitting a sleeve on an end portion of the second tube, which sleeveextends over the adjacent end portion of the first tube and has acircumferential step with a frusto-conical surface which engages thefrusto-conical surface of the ring on the side remote from the secondtube;

. welding the sleeve to the second tube at a location longitudinallyspaced from the end of that tube;

e. working the metal between the weld and the end of the tube thereby toreduce mechanically the thickness of the walls of the second tube toeffect differential endwise expansion of the second tube and sleeve andto clamp the collar between the ring and the end face of the secondtube.

2. A method as claimed in claim 1 wherein the ring is made from amaterial having a coefficient of expansion substantially the same asthat of the second tube and that of the sleeve.

3. A method as claimed in claim 1 wherein the ring is formed of amaterial having at least equivalent mechanical properties, in resistingcompression, to the second tube and to the sleeve.

4. A method as claimed in claim 1 wherein the frustoconical surface ofthe flange on the sleeve forms an angle between 60 and 45 with theinside surface of the sleeve.

1. A method of making an end-to-end joint between a first tube having athin wall and a second tube having at least at its end portion to bejoined a wall thickness greater than that of the first tube, comprising:a. forming the first tube with a collar around the end to be joined toabut the end face of the second tube; b. placing a ring over saidcollar, said ring having one face adapted to fit the surface of thecollar and the other face with a frusto-conical surface; c. fitting asleeve on an end portion of the second tube, which sleeve extends overthe adjacent end portion of the first tube and has a circumferentialstep with a frusto-conical surface which engages the frusto-conicalsurface of the ring on the side remote from the second tube; d. weldingthe sleeve to the second tube at a location longitudinally spaced fromthe end of that tube; e. working the metal between the weld and the endof the tube thereby to reduce mechanically the thickness of the walls ofthe second tube to effect differential endwise expansion of the secondtube and sleeve and to clamp the collar between the ring and the endface of the second tube.
 2. A method as claimed in claim 1 wherein thering is made from a material having a coefficient of expansionsubstantially the same as that of the second tube and that of thesleeve.
 3. A method as claimed in claim 1 wherein the ring is formed ofa material having at least equivalent mechanical properties, inresisting compression, to the second tube and to the sleeve.
 4. A methodas claimed in claim 1 wherein the frustoconical surface of the flange onthe sleeve forms an angle between 60* and 45* with the inside surface ofthe sleeve.